1. Field of the Invention
The present invention relates to an automatic status discriminator which can be mounted on a camera, unattended monitoring instrument, unattended recorder or monitor robot, and more particularly to an automatic status discriminator which can exactly discriminate the status of light illumination of an object or target to be observed (for example, a forward light scene, or a counter-light scene, i.e. a back lit light scene).
2. Related Background Art
Most new cameras have automatic exposure control devices (AE devices) so that users of the cameras can easily and quickly take photographs without being forced to make a troublesome exposure determination. However, in a camera with the AE device, there is no room for judgement by the camera user in determining the exposure and the AE device must have a function of determining photographing status. The determination of the photographing status includes a determination of a forward light scene or counter-light scene and a determination of a main object and a sub-object (for example, background) in the scene. As is well known, the exposures of the camera in the forward light scene and the counter-light scene must be set to totally different values even if the objects in those scenes are detected to have the same brightness. However, if the AE device has no function to discriminate those scenes, the same exposure will be given to both scenes and the photographing will fail to produce good results.
A camera with the AE device which has such a status discriminator has been proposed and put into practice. The status discrimination in the AE device of such camera uses a brightness comparison method. The AE device measures a photographing view field by a plurality of photo-detectors, compares the light intensity of a main object with the light intensity of a sub-object to determine if a photographing status is a forward light scene or a counter-light scene, and if it is the counter-light scene, a stroboscope is operated even in a daylight photographing mode or an alarm is generated to indicate need of stroboscope photographing mode.
However, since the known AE device having the above status discriminator pays no attention to a reflection coefficient of the object, it cannot exactly discriminate the status.
As is well known, the brightness of an article is proportional to the product of an intensity of an incident light to the article and the reflection coefficient of the article. Thus, if the brightness is measured, it includes the mixture of the intensity of the incident light to the article (which varies depending on forward light or counter-light) and the reflection coefficient of the article. It is, therefore, difficult, in some cases, to determine whether the object is in the forward light status or counter-light status, based on the measurement.
For example, if a main object is a man who wears a dark suit in a forward light scene with a light background and it is photographed, the AE device, in many cases, determines that the scene is a counter-light scene and a stroboscope is activated.
In the known AE device having the brightness comparison type status discrimination function, it cannot determine whether the reflection coefficient of a main object is low or it appears dark because of counter-light. Accordingly, if a photograph is taken by the camera with such an AE device under the situation described above, it is always photographed in a daylight synchronous photographing mode and a camera use has a feeling of unreliability of the camera with AE device.
Especially, the above defect is more pronounced as the size of the light intensity measuring spot to the main object is reduced. In the light intensity measurement, of the AE device, the smaller the size of the intensity measuring spot is, the more convenient to photograph a small object (or to far-distance photographing). Accordingly, the small size of the light intensity measuring spot is preferable. However, if the light intensity of a big object (or a far-distance object) is measured with a small area spot, the possibility that all over the light intensity measuring portion is overlapped with a simple pattern of the object increases, so that the affect due to of the reflection coefficient of the object increases. As a result, it is difficult to make a correct determination by the status discrimination system.